text:
Does useful load increase with more horsepower?
If an engine's horsepower is increased will max gross weight be increased?
For example what is the effect on max gross weight of changing the engine on a small GA airplane from 65hp to 100hp.

That is a certification issue.  It depends on what limits the particular max gross weight for that aircraft.  If the design happens to be limited by the max weight that the landing gear can handle, then hanging a heavier engine with a high HP, would not change the max gross, but would decrease the max payload.

First, you ask one thing in the title and another in the text of your question. Useful load is the sum of fuel and payload, whereas the gross weight is the force produced by the mass of the whole aircraft in the gravitational field of Earth.
First: Gross Weight
If you change engine power during airplane design, gross weight will go up. At that point, you will have relative parameters like wing loading (kg/m²) and power loading (kW/kg) defined and will size the aircraft accordingly.
If you switch the engine of an existing aircraft to a more powerful one, you will need to modify the airframe and systems if the aircraft had not been designed for the more powerful engine initially. Now your gross weight is already defined and cannot simply be changed. Let's first see what happens if a more powerful and heavier engine is fitted:

The higher engine mass will affect the location of the center of gravity and reduce the possible payload. Note that the mass increase will include a stronger engine mount and firewall, and possibly a balancing weight in the tail to put the center of gravity back into the legal range.
If you want to maintain the same power loading, you will need to increase gross weight, which in turn will increase structural loads. Now you need a heavier structure.

For now, let's assume that you stick with the old gross weight and reduce payload accordingly, because you do not want to rivet doublers all over the structure. Fine, but we are not done yet.

You might want to fit a larger propeller, which might require changes to the landing gear to keep a minimum ground clearance.
Your minimum flight speed will go up. If the aircraft is certified according to FAR part 23, the minimum speed should stay below 61 knots (see §23.49(d)). Maybe you will need to fit more effective flaps to keep the minimum speed constant.
Your maximum flight speed will go up. Technically, you can keep the limit speeds of the less powerful aircraft, but dive speed is calculated in one case by assuming 75% engine power (see §23.335(b)4i), so you will most likely be required to adjust limit speeds.
Once you raise limit speeds, structural loads go up. Now you need again to start riveting doubles all over the place.

You see, you cannot legally escape. Fitting a more powerful engine will require adaptions in the structure, and once you need to reinforce wings, landing gear and fuselage, you can as well choose a higher gross weight. But now you need to re-size the structure and re-certify the modified aircraft.
And we have not even started to look at the systems:

The bigger engine will have a higher fuel flow. Are the fuel pumps adequate, or will you need to switch them for more powerful pumps?
The higher design speeds might increase control forces, so now you need to modify the control system to avoid exceeding maximum stick forces (§23.143, §23.175)
Will the new engine excite new harmonics somewhere in the aircraft? Maybe now a part will vibrate and shake itself to pieces which had stayed calm and in one before?

The list goes on, but this shall suffice.
Now to your specific case: If you want to keep the power loading constant (which will give you the same performance as before), the airplane gross mass goes up by 54%, and so does the wing area.
If you want more performance, you will need to reinforce the structure (or start all over with a new design of the same size), and now it is up to you which gross weight to pick. The heavier engine and structure will eat into your payload and fuel, but if you accept that limitation, you can fly with the same gross weight as before.
Second: Useful load
As you can see from the first part of the answer, useful load is reduced by fitting a heavier and more powerful engine. Only when you re-work the structure to cope with the higher loads can you raise wing loading and regain the loss in useful load. Whether you can increase it by more than what you have lost so far depends on the maximum wing loading.
Let's assume for the rest of the answer that the outside shape (wing area, airfoil etc.) will stay identical to the original aircraft, except for maybe a bigger cowling, propeller and radiator.
The mass increase of the power plant plus its supporting structure is linear to the increase in performance. To beef up the structure, you could use the same percentage rule to stay on the safe side, but the real increase will be smaller. There are books which list parametric formulas for airplane masses, and those will show you the influence of the main parameters. They show that wing mass goes up with the square root of dive speed. Since speed is proportional to the third root of engine power, you will see that 54% more power means 15.5% more speed and 7.5% more structural mass.
Now let's assume that the propulsion system is 15% of the aircraft mass, and structural mass is another 40%. Your empty mass will go up by 8% (engine) and 3% (structure), and if your useful load was 30% of gross weight before, it will now be down to 19% of the same mass. Now we need to bump up the gross mass, and go for half of what you would gain if you keep power loading constant. This means your gross mass is going up to 127% of the original gross mass.
Before you rejoice that now your useful load has gone up to 46%, we need to account for the additional structural reinforcement that this gross mass increase produces. The parametric formulas give a structural mass increase proportional to m$_{gross}^{0.3}$ for the fuselage and m$_{gross}^{0.7}$ for the wing, and a higher wing loading will again result in a dive speed increase, so your total structure will now maybe weigh 15% more than before, for a total of 47% or 48% of the initial gross mass. Yes, your structural mass fraction will go up when you  increase wing loading! But still a sizable increase in useful mass should remain - you will now have 39% or 40% of the original gross mass available for fuel and payload, for a relative increase of 30% over the original useful load.
Now I never tried to keep minimum speed constant, but that would had complicated this answer even more. If the original plane had no or very simple flaps, this would be quite feasible, but result in almost a new wing design.

The short answer to your question is yes. However there are often other things involved than just increasing the horsepower (but anecdotally that has worked in the past). For example the Piper Cherokee line which goes from a 140HP all the way up through the Dakota which sports a 235HP engine on effectively the same airframe saw an increase in useful load as the horsepower increased (there were some aerodynamic changes that help over the years as well, like the swept wing that was introduced later).
There is a practical limit to this of course. First off there are engine size vs airframe limitations. For example you most likely can't bolt a Merlin engine to a Piper Cub frame (but I'm sure someone has considered it). There are also CG limits to take into account as your engine grows but airframe might not. CG loading can become an issue with very heavy engines up front.
In some regards wing loading will come into play here. Since a bigger engine will help you overcome drag and fly faster you can generate more lift and thus lift more.

Another limit is the stall speed (where maximum is specified by regulations) and take-off and landing distance (where not).

Cessna 140s can be fitted per STC rules with a Lycoming 0290D2 or 0290D or 0235 and do need extra weight in the aft section to get the CG right. Useful load goes down. The gross weight stays the same. Depending on many factors and perhaps operational safety one might get a gross weight increase approval for instance extra fuel if all other factors made it safe and reasonable. Most designs did not factor in larger than the engine used for the design and weight must have a certain "cushion of safety" like 150 percent above normal operating limits designed in. Certified VS Experimental and usage like holding out to the public for instance part 135 or part 121, racing planes etc. also effect allowable limits. Most basic a safety issue and thus a regulation effect concerning safety governs increases in gross weight.


text:
What are these acceleration parameters produced by the Inertial Reference System?
Following acceleration parameters are transmitted from Inertial Reference System (IRS) to Flight Control System (FCS):

Flight Path Acceleration
Along Track Acceleration
Cross Track Acceleration
Vertical Acceleration
Unbiased Normal Acceleration
Along Heading Acceleration
Cross Heading Acceleration

I only know acceleration based on the aircraft axis i.e lateral, longitudinal & Normal acceleration but what these acceleration parameters signifies?

Do you have specific IRS and FCS in mind? Or a link from where these names come? I suspect there are alternate names for each of them.

"track" is the direction the plane is flying, "heading" is direction it is facing (they differ due to wind and side-slip). The track ones would certainly be in horizontal plane, but I am not sure whether the heading ones would be in horizontal plane or aircraft plane. The ones in aircraft plane seem to be more useful, but those would be better called longitudinal and lateral. I would guess unbiased normal means normal with gravity subtracted. But I have no idea what the flight path one might be; my only idea was vertical, but that is a separate item.

Looks like they came from here.

@Jan Hudec: Yes Specific FCS & IRS but cannot name the project.
Longitudinal, lateral & Normal accelerations are transmitted by IRS along with these all accelerations. I think these accelerations may be somewhere computed from GPS in IRS and transmitted to FCS

@ToUsIf: That confirms that the heading ones are in horizontal plane just like the track ones.

@ToUsIf: The primary source of acceleration in IRS is the accelerometers and gyroscopes. GPS is only used to correct drift of the position calculated by dead reckoning, that is integrating the velocity calculated by integrating the accelerations. This is much more reliable as it can't be affected by basically any outside factors and has better temporal resolution. GPS only gives 1 position a second, which is good enough for navigation, but not AP or FBW.

I can't be sure without seeing actual documentation of the thing, but I would expect:

Flight path is direction of the total velocity vector, i.e. the direction the plane is flying, in Earth-relative frame of reference. This differs from direction of longitudinal axis by alpha (angle-of-attack), beta (side-slip) and wind.
Track is projection of flight path to horizontal plane.
Heading is projection of the longitudinal axis to horizontal plane.

Then:

flight path acceleration would be simply acceleration along the flight path
along track and across track are, well, along and across track as defined above.
vertical is vertical; should not include gravity, so when maintaining vertical speed it should be 0.
unbiased normal acceleration is most probably what is also called inertial normal acceleration, that is acceleration without gravity.
along and across heading are, well, along and across heading as defined above.

This is almost correct, except for two points. Wind has no bearing on the difference between the longitudinal axis and the flight path; only alpha and beta do. "Flight path" means the path of flight through the air. Also, "vertical acceleration" probably means acceleration along the local gravitational vector ("up"). "Normal" means perpendicular to the flight path. These two are only the same if the aircraft is at zero pitch and roll. So an airplane doing a loop at constant airspeed, at the moment of 90° pitch, has positive normal acceleration but zero vertical acceleration.

@dvnrrs: At least in Airbus there is a "flight path angle" mode in autopilot and this definitely means flight path angle relative to Earth, not wind.

Further comment: the reason for all these different definitions/measurements is ease of consumption by the flight guidance system. The designers of the "control laws" for autopilots use these values in various ways as feedback, as a way to detect and reject spurious commands due to turbulence, etc. Each control law and each situation requires a slightly different parameter. The "norm" is for the data producer (AHRS, IRS, whatever) to do all the number crunching so that all the FGC has to do is select and use whatever value's appropriate for the situation.

@dvnrrs: And the more important argument, IRS has no clue about anything relative to wind. IRS is inertial reference system, which can measure position, velocity and acceleration to inertial reference frames, which Earth is to sufficient approximation. It is calibrated relative to Earth during start up and thus all the values are relative to Earth - or the plane, but never the wind.

That's true, but just a terminology conflict. Airbus' FPA mode just maintains a constant angle relative to horizontal (to, say, descend along a 3° slope). It's not the same as what an AHRS/IRS means by "flight path acceleration." (I write software for Level D flight simulators and have detailed knowledge of avionics data parameters.)

@dvnrrs: Would you then be so kind and formulate full answer? You seem to be more knowledgeable than me.

let us continue this discussion in chat

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
Dash-8 Speed momentarily drops on takeoff
I was on a Dash-8 back in July and August.  Looking at Flightradar 24, the speed is non constant and very choppy.  It even goes down momentarily during the takeoff process.  I believe that the Dash-8 does not have auto-throttle if that makes a difference.
Is this normal for this aircraft, or do I have bad data?

The KGC end of each trip is unavailable probably due to a lack of infrastructure at a very remote airport.

You were on the airplane... did the acceleration feel like they were slamming on the brakes at times (which is what it would take to reduce speed gain to zero or negative) followed by strong bursts of speed? Or did it feel like a constant & relatively even acceleration the whole time?

I'd also add that winds aloft can change as the airplane climbs, resulting in varying ground speed for a constant airspeed. Similarly change in heading can also drastically change ground speed (e.g. taking off south into a 20 knot headwind which turns into 20 knot tailwind when turning on course to the north would cause a 40 knot change in ground speed).

The aircraft ground speed will continuously increase during the takeoff roll and then remain constant or only change slightly during the initial climb. The speed should never decrease during these stages of flight. Airspeed can vary a bit during the takeoff, e.g. caused by a sudden gust of wind. This might result in "choppy" airspeed data, but due to the inertia of the aircraft not really ground speed. FR24 always shows ground speed and may sometimes also include airspeeds (see Understanding Extended Mode S Data in Flightradar24 for more details).
The ground speed and even the position shown by FR24 can have inaccuracies due to the way it is determined. We already have a few questions here that cover the details, e.g.:

Why do aircraft on Flight Radar 24 jump around randomly sometimes?
Why did the Flightaware groundspeed readout suddenly spike for this flight?

Update after seeing the FR24 screenshot:
The groundspeed during the takeoff roll is actually quite smooth and increases continously:

The slight decrease in ground speed during the climb could be the result of a change in wind speed or direction, possibly caused by turning into a different direction after takeoff.

Regarding the Dash-8, you said

I believe that the Dash-8 does not have auto-throttle if that makes a difference.

That is true, the Dash-8 does not have autothrottle. But at least the Q400 variant has FADEC (full authority digital engine control). For takeoff, the pilots will smoothly advance the power levers into the rating detent.
The FADEC then controls the engines to produce the rated power, typically NTOP (normal takeoff power):

The power lever system is used to initiate power demand through the Full Authority Digital Elec-
tronic Control (FADEC) to meter fuel to the engine in the forward and reverse ranges. [...]
Power lever movement between FLIGHT IDLE and RATING results in the FADEC modulating
the power proportionally between flight idle power and the selected rated power.

(Dash-8 Q400 FCOM - Powerplant)
The Q400 can also reduce the takeoff power when full power is not needed:

Prior to take-off, the power may be reduced for take-off in the NTOP rating using the power der-
ate function. To decrement (or derate) the requested power, the pilot presses the DEC discrete
with the condition lever at the 1020 RPM position (NTOP rating) and the power lever below the
rated power detent. Selection of the DEC discrete, which is a momentary switch, decreases the
NTO requested power in steps of 2% to a limit of 10%. The selection of the Power Derate
RESET discrete at any time resets the derate to 0%.

(Dash-8 Q400 FCOM - Powerplant)
This system ensures a smooth and constant power for takeoff. It is actually quite similar to how it works in modern Airbus aircraft, which have autothrust. The thrust levers are placed into the TOGA or FLEX/MCT detents for takeoff and the FADEC does the rest. Autothrust is not used for takeoff.

+1 but "Airspeed can vary a bit during...", I beg to differ on that. Airspeed can vary alot during takeoff or approach/landing if it is gusty. This will of course be compensated for to keep flying safely, for example by adding half the gust speed to target speed.

@Jpe61 A gust of 20 kt will change airspeed by ~20 kt. Compared to typical takeoff speeds ~120 kt for the Dash, it's not that much. And I wouldn't take off in 120 kt gusts :D  Unfortunately, the OP didn't mention how "choppy" the speed data is in the FR24 recording.

I consider a sudden change of ~15% a lot. We can agree to disagree on this.

If the reported speed is GPS speed then I know experimentally that this is speed in the horizontal plane (for the GPS types I’ve checked), so if the climb is steep then you might see a reduction in groundspeed with no reduction in airspeed.  In the extreme case if the aircraft ascends vertically then the groundspeed will be zero.

@U_flow Takeoff roll for the Dash should be around 25-30s and typical takeoff speeds are around 120kt (~140mph). Seems perfectly normal to me.

@Bianfable yes looking at it again, that is probably correct. First the taxi, then the acceleration to take-off speed. I will delete my other comment.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Are auxiliary fuel tanks optional on the Boeing 737 Max 9?
Does the  Boeing 737 Max 9 have auxiliary fuel tanks like the Boeing  737-900ER? And have any airlines ordered them without if optional?

Aux fuel is optional on the Max 9, but to find out who has ordered aircraft with and without you will have to coax that information from Boeing or the airlines operating them.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What does this term in a SimBrief flight plan routing mean?
I checked everywhere and I cannot figure out what the bold sections mean in this flight plan routing I got from SimBrief:

DTTA/11 N0430F360 TOBI3C TOBIB UA725 TANIT UM733 OSMAR DCT ALEDI DCT APSUX DCT GILIO DCT NUKNI DCT SOVUB/N0347F180 Z43 OTGIG OTGI2E LIPZ/04R

I understand that this may be related to some flight level but the first section before the F does not seem to make sense to me.


text:
Why is the missed approach point sometimes beyond the threshold or runway like in the example below?
Why is the missed approach point beyond the threshold or sometimes beyond the runway like in the picture below? Is it just to simplify the ATC job or prevent routes from crossing or is it procedural?

The missed approach point (MAP) needs to be identified somehow by the pilot flying this approach.
The example you show is a VOR approach that requires neither RNAV/RNP capability nor DME. That is also why you see a duration (3 Min or 2 Min) for the outbound leg instead of a fix (there is an optional RNAV fix [FS044] that may be used if you are RNAV capable, but it is not required).
The only point that can be identified here is the VOR itself. Therefore, the procedure is constructed with the VOR as the MAP, even if that happens to be after the runway. Note that you can execute a missed approach earlier than the MAP (that is the latest point, where you have to execute it).
If you look at the similar VOR Z Rwy 04 approach with straight-in minima, you see DME required at the top, which allows defining a MAP before reaching the runway via DME:

What advantage is there to flying the VOR Z (with DME) instead of VOR A (with stopwatch)? Or more to the point maybe, what advantage is there to publishing it? Are the minimums lower for the VOR Z? If so that might be something to include in the answer/screengrab.

@randomhead Yes, the VOR Z has lower straight-in minima (900'), the VOR A is circle-to-land only. Not sure how that's relevant for the answer though...

Not strictly relevant but I think it would add to overall understanding.

@randomhead Modern avionics automatically show the distance to the next fix (via GPS substituted for DME), which is a lot easier for the pilot than a operating a stopwatch and doing math, especially when hand-flying the plane.


text:
Why do VOR A, B charts only have circle-to-land minimums, while VOR X,Y,Z charts have straight approach minimums too?
Why do VOR A, and B charts only have circle-to-land minimums, while VOR X, Y, and Z charts have straight approach minimums too? Is this the only difference and is it only used to separate the two chart types?

Yes, that is the difference. From the FAA's Instrument Procedures Handbook, Chapter 4:

Straight-In Procedures
When two or more straight-in approaches with the same type of guidance exist for a runway, a letter suffix is added to the title of the approach so that it can be more easily identified. These approach charts start with the letter Z and continue in reverse alphabetical order. For example, consider the (RNAV) (GPS) Z RWY 13C and RNAV (RNP) Y RWY 13C approaches at Chicago Midway International Airport.

Circling-Only Procedures
Approaches that do not have straight-in landing minimums are identified by the type of approach followed by a letter. [...] As can be seen from the example, the first approach of this type created at the airport is labeled with the letter A, and the lettering continues in alphabetical order.

In actuality the circling approaches are named such that the suffix is unique across all airports with the same name within one state, and unique across all airports serving any one city, as laid out in this Av.SE answer.

Thank you very much for your answer. I would also like to ask, why does Jeppesen create a separate chart just for circle-to-land approach, even though VOR Z, Y, and X charts already have circle-to-land minimums?

@pilot162 Small point, but Jeppesen "creates" no approaches; each national government (i.e. the FAA in the US) creates the approaches.  Jeppesen prints them in a standard format, distributes them in both paper and electronic media, and does a number of extremely useful things in that regard, but the approaches are created by somebody else.  They publish whatever information the FAA gives them in terms of courses, waypoints, minima, etc.

So let me ask, why does someone (the national government) create a separate approach (VOR A,B) for circle-to-land even though there are circle-to-land minimums specified in the VOR X,Y,Z charts (approaches)?

@pilot162 Sounds like another question. Please include examples.

@pilot162  The VOR-A (and similar early-letter) approaches are probably older than approaches with a late letter to a given runway (i.e. VOR-Z runway 32).  As to why not get rid of a "VOR-A" when a "VOR-Z to 32" could have the same circling mins, that's going to be specific to each airport... perhaps the VOR-A is build so that it can be flown with less equipment (no DME, perhaps) or less missed approach performance required than the Z.  But it would be up to the individual airport to ask the FAA to decommission a particular approach, if there were a need to do so.

That makes a lot more sense, thanks for the comment. I will create a separate question title for this question.

@pilot162, if you read the FAA IPH I linked, it explains why some approaches are not able to have straight-in minima. The most obvious example is when the final approach course is not in line with a runway!

I know the conditions and rules that should use circle to land instead of straight in landing. What confuses me is why even though there are circle-to-land minimums on charts at airports where straight-in landing is possible, only circle-to-land charts or approaches such as VOR A, B are created. (For this reason, I will find a chart example and share a new question.)


text:
What are these blue lines around the runway at the airport chart that I marked with red line?
What are these blue lines around the runway at the airport chart that I marked with red lines? They are not waterways or taxiways so what are they?
Yenisehir Airport (LTBR):

Adana International Airport (LTAF):

Adana International Airport and Yenisehir Airport from Turkey. I've seen these blue lines several times on different charts. LTAF and LTBR btw.

And this is why you have to look out the windows when flying IFR. A glance a reality can tell you what charts & instruments won't.

They are in fact waterways: irrigation ditches or channels. The Jeppesen airport chart legend lists them as

32 — Ditches in the vicinity of the airport are depicted.

For example, looking at a Google Maps view of LTBR, the blue line charted west of the runways clearly refers to the Kurutma Kanali/Marmaracık Gölü Kurutma Kanali. The blue lines between the runways are not shown on the Google Maps terrain/relief view, but switching to the aerial imagery view reveals a drainage ditch on either side of Runway 07L. In fact there appears to be another one which Jeppesen does not depict on the south side of Runway 07R.

Thank you so much for your answer. Actually, the reason why I asked the question was the blue line between the runways, because there was nothing like a waterway between the runways while flying at that airport. But as a result, as you said, it becomes clearer when you check it from Google maps.


text:
Why are flight instructors in the US called CFIs?
I live in EASA-land (Europe), here we call our flight instructors simply that, "FIs". That they hold an instructors certificate is simply implied. Why are flight instructors in FAA-land (US) called CFIs? Is there any historical reason why the "C" is always added to the abbreviation, e.g. in the past there was a difference between certified and non-certified FIs (if there ever was such a thing)?

I would imagine that it's because at one point in aviation history, there were no such things as "certified" flight instructors.  Much as in many places in the US, one can set up as say a driving instructor without any formal certification.

Certified flight instructor = CFI. Add a multiengine rating to your CFI and now you are a multiengine flight instructor, or MEI. An instructor with single and multiengine instructor ratings is commonly referred to as a CFI/MEI.  What if you are a CFI but only in gliders?  CFI-G is the most common shorthand.
Pilot authorizations are specifically called "certifications" in the US, not "licenses."  My guess at the inclusion for the C in CFI is that any pilot can provide instruction but only appropriately certified and rated instructors can provide training that can be counted for a student's training for a new certification, flight review, or whatever.

I guess that makes total sense and nicely shows the subtle differences between European and American mentality. The American being more practical, as by nature every pilot can instruct another person, thereby necessitating the need for the C in CIF, where as Europeans would always think you need some licence/certificate first before you give somebody advice ;)

Actually, in the US, the accepted term for a flight instructor by the FAA and the general aviation (not to be confused with General Aviation) public is Certificated Flight Instructor (CFI). An instructor for instrument ratings is called a Certificated Flight Instructor-Instrument (CFII). This is opposed to a Basic Ground Instructor (BGI) or an Advanced Ground Instructor (AGI).
Although these terms are not defined in Title 14 of the Code of Federal Regulations governing aviation, they are used extensively thought out this document. So is the term authorized flight instructor (which is defined). People may have simply followed the lead of the predominant legal authority.

Dean, normally I love your answers, but I beg to differ.  And so does the FAA, in their on-line glossary here:  https://www.faa.gov/jobs/abbreviations/#tab-C

Thanks @MichaelHall. Same here. Like I said, the term is accepted by the FAA. But, I have yet to see it defined in the FAR/AIM. Although, there are a lot of terms prescribed for use that are not defined in the FAR/AIM. Thanks for the reference, though. I greatly appreciate it, and will bookmark it.


text:
Where can I find information on the DC-9's turn radius in flight?
Does anyone know where I can find information on a DC-9-30's turn radius at various altitudes and airspeeds?  I've tried Googling it, but all I've found is information about its turn radius while taxiing.

No different from any other jet.  Use this turn radius calculator http://www.csgnetwork.com/aircraftturninfocalc.html

Unfortunately, "[t]his calculator DOES NOT take into consideration wind speed or direction, temperature, air density or aircraft performance and assumes LEVEL flight and turns", and I kinda need to be able to take those factors into account (it's for a short story I'm thinking of writing, and I need it to be as realistic as possible).

@Sean, if you want to take these things into account, you have to specify them. Very, very precisely. And also specify what you actually mean by turn radius, because once wind is involved, you can be using wind-relative or ground-relative frame of reference and the results will obviously be different in each (and the turn will not really be a circle in the ground one).

@Sean, I believe you can account for density by simply giving all the speeds as TAS valid for the desired density altitude.

@JanHudec: The specific scenario I have in mind is DC-9-32, ground-relative turn radius, 10-knot wind, temperature 85F, altitude 10,800' AMSL, 260 KIAS.

@Sean As a constant wind from one direction distorts the turn, speaking of ground-related turn radius doesn’t make much sense in practice, I‘d say - it constantly changes throughout the turn. If you specify wind direction and speed (assuming constant wind) as well as bank angle used for the turn and aircraft heading before and after the turn, one can model the ground track, if that helps?

@CptReynolds: Yes, that'll do (wind from 115 degrees at 10 knots).

@Sean Well, as I said, you’d need to specify wind direction, wind speed, aircraft heading before and after the turn, and the bank angle you‘d like to use (normally in airliners up to about 25° depending on the situation), and whether you‘d like a constant bank angle or something else (e.g. flying the turn to intercept a given course from/to a navigation aid) etc. If you want high detail, you need to specify at a detailed level, please. If you decide that, in fact, that level of detail isn’t required for the story after all, then anything that turn radius calculator can generate will be fine.


text:
Is there any way to estimate the weight difference between a trimmable horizontal stabilizer and a fixed tailplane?
I am trying to estimate the benefits of using a trimmable horizontal stabilizer (THS) instead of a fixed tailplane. In my model I use a T-tail (Sh~30 m), and I can trim the aicraft in every condition so the main reason to go for a THS would be aerodynamic efficiency.
I've estimated the drag reduction but I'm having huge problems estimating the weight increment of the system.
Please, could someone shed some light on this? I've checked a lot of references but still couldn't find anything clear.

Hard to find a general reference for this one. You're adding the weight of the hinge, the actuator, and the supporting structure now connecting only to the hinge axis.
Torenbeek section 8.4.1 gives a weight estimation for preliminary design purposes for the tail group of high subsonic aircraft: it mentions a weight increase of 10 % over the weight of a fixed horizontal tailplane.

Thank you! I looked in the Torenbeek but missed that!

You need a trimmable stabilizer in two cases:

In transsonic flight when local shocks render the elevator ineffective, or
In case of powerful flaps which require a wider trim range than what a regular elevator can provide.

If you can get by with a fixed tailplane, not only the weight saving but also the reduced complexity should be weighed against the increase in efficiency. If your elevator trim deflections in climb and cruise are within single digits, the drag increase is negligible. If you need more trim deflection during approach, the drag increase might even be welcome.
Make sure that with all trim deflections your elevator maintains sufficient control authority. Then a fixed tailplane is the best choice. The weight increase versus efficiency calculation should only decide wether to use a trimmable stabilizer or not if you need to achieve a specific performance figure. Normally, the extended trim range is what is pushing engineers to choose a trimmable stabilizer. If it is not needed, it is better avoided in order to ease maintenance and to avoid the new failure modes which come with more moving parts.

Number 1 won't be a problem.
However, I see the other points differently.  I have control to trim the aircraft with a maximum of approximately 2/3 of the maximum deflection (~15º) in the worst-case escennarios. I think the other 1/3 (~7º) would allow me maintain sufficient control (maybe this is the first point where I am wrong).
I have  mainly analysed the drag in cruise and, as I see it, an elevator deflection would have a significant effect increasing the pressure drag of the HTP. Let's say it reduces by 2% the overall efficiency just in cruise.

Also, I strongly believe a THS is also a strategic decision:
-It allows you to move more the CG.
-It allows you to create derivatives of your design.
Apart from that, It also reduces loads in the elevator and allows the pilot to maintain full control authority when the aicraft is trimmed (which I assume it much more safer).
Of course, this is just my opinion and I may be completely wrong.
Again, thank you for your time and help :)

@JavierGarcia: If you feel you need a wide cg range, then you do need a trimmable stabiliser, as I said. And 15° just for trim will not leave enough for control.

Thank you sir! I'll think in what you said and try to make the best decision

Excuse me sir,
Please, could you tell me what elevator deflection is common in take off and landing manoeuvres? Do aircraft only use the THS for these so they still have the whole elevator deflection available? Thank you!

@JavierGarcia: Yes, with a trimmable stabilizer you want to trim the aircraft such that it will lift off by itself once the forward pressure on the yoke/stick is relieved. Total elevator travel in this case will only be a few degrees. More is needed to correct for sudden and violent gusts, but most (and all slow) corrections are done with the stabilizer incidence. In case of landing elevator travel can be higher, but rarely above 15°.

Thank you so much! I hope one day I know as much as you about aircrafts ^^

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What does flight ID mean here in the picture? It stated in brackets for Performance
What does flight ID mean here in the picture? It is stated in brackets for Performance. I searched but couldn't find an answer. I would be glad if you help.

Since you tagged diamond-da40, I assume this is about the G1000 avionics as installed in the DA40. The manual for that G1000 unit is available on the Garmin website. According to the manual, the Flight ID is the aircraft identification transmitted by the Mode S transponder:

4.4 GTX 33 MODE S TRANSPONDER
The GTX 33 Mode S Transponder provides Mode A, Mode C, and Mode S interrogation and reply capabilities.
Selective addressing or Mode Select (Mode S) capability includes the following features: [...]

Flight ID (Flight Identification) reporting – The Mode S Transponder reports aircraft identification as either the
aircraft registration or a unique Flight ID.

As to why it is under the Performance step: the flight ID is entered on the Timer/References Window, which is the same window where the speed bugs are entered. So it makes sense to have it on this step:

That was a very comprehensive and descriptive answer, thank you very much.

The callsign being used for this flight, which will then feed from the FMS into the Mode-S transponder. This is how FlightRadar24 tags your flight.

I suspect this is indeed the correct answer. Question remains: why is it listed under performance? It could fit under flight plan (where the Flight ID is defined) or Radios (because the Flight ID is going the transponder, which is a fancy radio transceiver). With performance, the Flight ID has no relation.


text:
What is this black teardrop-shaped object under the C-47 Skytrain cockpit?
I was recently at the Airborne Museum in Sainte-Mère-Église, France, and I saw a C-47 Skytrain for the first time in person. I saw that, under the cockpit, there was a black, teardrop-shaped object. I couldn't figure out what it was.

What is it, and what is it for?

Related: What is the vertical rod on this Swissair DC-3 drawing?

According to the following cutaway (source) that's simply the fairing of the ADF (automatic direction finder) antenna (number 24):

Within the fairing

Very informative picture.  I can now improve the description I learned many years ago for the C-47 / DC-3 / Dakota.  I can now call it "A collection of one hundred and thirty-five parts flying in loose formation."  Citation for the "Collection of parts" reference: https://www.bbc.com/culture/article/20131009-dc3-still-flying-at-70

I suspect there's a little more than 135 parts.

@ceejayoz 135 Spanish line items, perhaps ?

Call it 136 then: all the above, plus: "136: Miscellaneous"


text:
How are compressor maps drawn?
I've always thought they are empirically derived: once you have your axial compressor phisically in a bench, you set both a rotational speed and a mass flow throught the turbomachine then you measure the pressure ratio so you can fix a point on the map. After, It will be made for several mass flows therefore defining a particular constant speed line.
It is correct?

(image source: Wikimedia)

From my textbook, Fluid Mechanics and Thermodynamics of Turbo-machinery by Dixon, it is explained that they find the results for the working line empirically. This corresponds to the line with the black dots on the diagram you provided.
Essentially, your test rig is made up of a compressor that is connected to a downstream throttle. It is the size of the throttle (in a real engine, this corresponds to the size of the nozzle) that is going to determine the test working line (called an operating line if it does not pass by the Design Operation Point). In other words, a different operating line corresponds to a different size throttle.
Then you vary the speed and measure the obtained pressure ratio. Connecting the dots will give you the working line.
ADDED DETAIL:
You have to know the size of the throttle because it will give you valuable information regarding your exit configuration. This has to do with the fact that the nozzle will usually be chocked, which will fix your non-dimensional mass flow through the nozzle. But that's a whole other topic in itself!
I did my best to answer your question, sorry if it does not help, I am only a student! If you want details of the calculations for compressor maps, you should check out chapter 5 of Dixon.

I believe what Hypatie D'Alexandrie has stated is correct. To add to this, I would like to mention that nowadays as we are getting more computational, there are few softwares like Gasturb and GSP which allows to simulate and analyze the performance of gas turbine components in any kind of configuration for in steady and transient state by assuming 0-D modelling of thermodynamic cycle i.e. by taking the average of the properties across the flow sections.
With many companies using these kind of softwares, I have heard this has made them shut down huge test rigs which were specifically designed to perform tests and also draw characteristic maps. For example- RR doing that in Derby
As far as the operation line/working line is concerned, it is essentially a collection of points on each constant speed line at which the condition of power equilibrium is satisfied i.e. the bet power output is equal to the power given at the given set of conditions, without acceleration or deceleration. The Design Point (DP) is always on the constant speed line of 100% and speed lines at left or right are representational of the spool speed lower & higher than the DP.


text:
What is the range difference between LEAP and PW1000 powered A320 and A321 NEOs?
Mounted on the same aircraft, PW 1000G and CFM LEAP are two very different engines, with different performances, that should have an impact on range. And we know range is a very important aircraft parameter, since Airbus is developing longer and longer range versions of the A321.
So what is the difference in range on the same aircraft between the two engines?

It basically boils down to the thrust-specific fuel consumption of the engines. Wikipedia has a table for various engines, but as far as I can tell, the values for the new LEAP and PW1100G are not publicly known.

According to Airbus
Airbus quote a single range figure of 6300km for the A320neo
This is 100km more than Airbus claim for the A320ceo with sharklets but the difference is probably due to increased fuel capacity in the A320neo and possibly to revised wingtip arrangements.
The difference in range between older A320 (~5700km?) and A320 with sharklets (~6200km) appears to be 500km. This implies the wing sharklets are more important than larger fuel capacity and both these features are more important than engine differences alone.
Superficially at least, the choice of engine does not affect the range claimed by Airbus.

This raises the question, what benefits are provided by the new engine options alone?
The only relevant claim by Airbus appears to be

The A320neo also offers significant environmental performance with nearly 50% reduction in noise footprint compared to previous generation aircraft.

I guess airlines choose between NEO engine options mostly based on commercial factors and maybe on fleet characteristics, maintenance arrangements, etc. Factors other than range.

According to others
Forbes has a comparison beween these two engines which suggests the geared-turbofan arrangement of the PW1000 offers large advantages in both fuel efficiency and noise.

According to the Airbus page, the NEO has only 100 km higher range, but a 1 t higher MTOW and 470 l less fuel. Also, both aircraft actually exist in many variants with slightly different MTOW and fuel capacity, so direct comparison is difficult.


text:
aerodynamic forces on an engine cowling
In Mendenhall's book about the Gee Bee racers, he describes that on the Models Z, R-1, and R-2, there was a strong tendency for the engine cowl to get pulled forward and into the prop during races, requiring reinforcement of the cowl attachment points to the engine & airframe- which puzzles me to no end. Can someone please explain the pressure distribution right behind the prop that would cause this?

IF that's the case, then there must have been an imbalance of  pressure on the forward and back side of the cowling.  It might be more intuitive to think about the cowling being pushed forward from high pressure behind the cowling than being pulled.

On airplanes with sliding teardrop bubble canopies, the aerodynamic forces can sometimes push the canopy forward and if they are unlatched they just sit there.

I have not done any sort of aerodynamic analysis of this but I'm speculating that another factor might be a lower-pressure region behind the center area of the propeller caused by the centrifugal force of the swirling airflow.  This is likely negligible for "normal" propeller-driven aircraft but the GB racers push the envelope of performance.

This has a lot to do with proper understanding of engine compartment air flow and should be studied further.

You are looking for 'cowl lip suction' or 'lip thrust'.  This is a phenemona that also happens on jet engine cowls when they have lots of spillage.
When the cowl flaps are (nearly) closed, the engine bay approaches stagnation pressure.  Many of the streamlines that would otherwise go into the front of the cowl instead are diverted around the outside -- this is a situation similar to engine spillage (when mass flow can't go through the engine, it goes around).
This air is forced to rapidly accelerate around the cowl lip -- this region of high acceleration leads to high velocities which lead to a local suction.
Here is a panel code solution demonstrating this.
The magenta represents the inside of a blocked engine -- the pressure there reaches the stagnation pressure for the flow.
The green and blue around the cowl lip represent high velocities and strong suction pressure -- some of that area has a forward-pointing outward normal vector.  This means that the local suction will resolve into a thrust.
If the cowl were truncated somewhere on the constant-diameter section of this nacelle (and you can imagine the entire engine compartment is at stagnation pressure (magenta) then you can see how the cowl would have a net forward force on it.

Rob, really appreciate your explanations, and I followed this up until the last sentence, which seems to suggest that the right shape can provide thrust for free (once whatever speed is initially attained). Does the "net forward force" exclude the rearward force on the magenta area, or is something else going on here to preclude the free lunch scenario?

@RalphJ "this region of high acceleration ... leads to local suction", you know, like wings and propellers?


text:
Does the aerodynamic center move when flaps and slats are deployed?
Does the aerodynamic center of an aircraft move when flaps and slats are deployed?
I am trying to figure out if the AC of an aicraft moves with landing and take-off configurations. I know Cl and Cm change a lot, but I can't find a reference where the movement of the AC is discussed.
I've checked Roskam, Anderson and Aerodynamic Characteristics of Wing Sections and it seems like the AC position doesn't change only with flaps but they don't show examples of wings with flaps and slats.

Better read Fluid Dynamic Lift, chapter 5, section III. This should answer all your questions.

The aerodynamic center does not move when plain or camber flaps are used. A plain flap will only change the camber of the wing and, therefore, will only affect its zero-lift pitching moment. Flaps have their own aerodynamic center, and their lift change should be summed up in the flap's aerodynamic center.
Note that the aerodynamic center of the aircraft is used for the lift force change resulting from a change in the angle of attack while the flap aerodynamic center is used for the lift force change from a change in the flap's deflection angle. With flaps deployed, a change in the angle of attack will still cause a lift change which acts on the aircraft's aerodynamic center! Only the constant pitching moment around the aerodynamic center will change with flap deflection, and in order to calculate this moment, assume the lift change from flap deflection to act in the flap aerodynamic center.
The location of the flap aerodynamic center changes with the relative chord of the flap. For a flap approaching a relative chord of 0, the theoretical flap aerodynamic center is at 50% of the wing's chord. With increasing flap chord the flap aerodynamic center moves forward proportionally with the flap's chord increase until it reaches the 25% chord point for a flap of a relative chord of 1 (a full-flying control surface, in other words). See Figure 46a from chapter 5 of Sighard Hörner's Fluid Dynamic Lift for proof.

Flaps which increase the wing's area will of course shift the neutral point in proportion to the change in the wing's chord effected by the flap.
Slats may be viewed like a slat-sized wing followed by a wing-sized flap and an incidence change equal to the slat's deflection angle.

Thank you for your answer! It seems like I'll need time to understand it completely

Yes the AC changes when flaps are deployed. Torenbeek has a section on change of pitching moment as a function of flap deflection in Appendix G, section G-3.3.b. The methods described are empirical, based on statistical information and on Glauert's linear thin airfoil theory.
The shift in pitching moment is of course highly dependent on the type of flaps used, the deflection, trailing edge flap span, wing sweep, and change in wing camber and chord extension.
The author has a chapter on leading edge devices as well, for which he signals a lack of empirical data. There is no section for AC change as a function of leading edge flap deflection.

Yes, it seems like everyone estimates the change of pitching moment but neglect the changes in the AC position.  That is what I've done but I like to be sure about the real AC position.
Thank you for your answer :)

Um -  a change in pitching moment is a change in AC.


text:
How do CFIs typically determine proficiency for complex and high-performance endorsement?
I'm working on getting checked out in our flying club's Arrow II. Our club's insurance requires 10 hours of instruction if you don't have any retractible time.
I've done a few hours with an instructor, and he signed off on my complex endorsement, which I also need from an FAA standpoint. So I'm FAA endorsed, but I need more time to satisfy club insurance.
§61.31.(d)(2)(e)(i) says:

(i) Received and logged ground and flight training from an authorized instructor in a complex airplane, or in a flight simulator or flight training device that is representative of a complex airplane, and has been found proficient in the operation and systems of the airplane;

What defines "found proficient?" What is the list of things an instructor "ticks off" their list to be able to give that endorsement?
Same question for the high-performance endorsement?

The FAA does not provide "endorsements", instructors do. The FAA allows instructors to provide these endorsements based on the instructor's evaluation of the pilots proficiency. So you are not "FAA endorsed", you are instructor endorsed which the FAA recognizes.

I apologize if I did not word my question precisely enough for you. An instructor 's endorsement makes me compliant with FAA regulations.
My question still remains unanswered.

There is no regulation that I can find that defines "proficiency". It is up to the instructor to determine that you are proficient. Whether this takes 1 hour or 10 hours is entirely up on what the instructor wants to see to make that endorsement. This is a similar reason why some people solo at 5 hours and others 30, the pilot is part of that, the other part is how comfortable the instructor is and what the instructors comfort level is.

No need to be grouchy @JimJarrett, Ron was making sure the question was understood. A simple answer is that if an instructor signs you off then you have been found proficient.

Welcome to aviation.SE! See this question for details of the high-altitude endorsement. Unlike the HP and CMP ones, it does have specific training requirements.

This Advisory Circular describes what should be examined when transitioning (and ultimately endorsing) a pilot for complex operations.

This publication is offered as a guide to the procedures and standards
  to be followed for a thorough and comprehensive checkout in these
  airplanes. The conscientious application and adherence to the scope of
  coverage recommended in the syllabus should result in a more
  competent, effective, and efficient pilot.

The document is fairly short and I suggest you look through it, for brevity I wont copy it here as its pretty much all relevant. Its important to note that this is simply what the FAA suggests (albeit strongly) and its not required all the described things be covered in a checkout. Although the instructor may be assuming some liability by signing you off without a proper checkout.

As I understand it, 61.31 provides the legal guidelines for doing so, but the FAA prefers CFIs to only sign someone off on a complex or high performance airplane when they can handle the airplane at or above the practical test standards for their pilot certificate eg maneuver the airplane +/- 100 ft, +/- 10 kts, etc.
As Jim Jarrett states, while these are the standards the FAA wants to see, insurance companies are a totally different animal.  Underwriters have paid out too many claims from a numbskull bellying an airplane in while ignoring the gear warning horn and will set minimum hourly requirements for flight clubs to rent complex aircraft out.


text:
How should I request flight following when I'm not taking a direct route to my destination?
I want to plan a flight from KMSN - KDAY. My plan avoids the ORD airspace as much as possible, so something like:
KMSN - JVL - KARR - JOT - EON - KRZL - OKK - MIE - KDAY
What would be the phraseology to use to get VFR flight following to let ATC that I'm not planning the most direct route?

You should file a flight plan and open it with FSS (or via an app). You can request VFR flight following which will provide radar services (if available, you may not get it, be aware). You should just have to tell ATC where you are heading, not that you necessarily need to land there. Hopefully one of the ATC controllers on here can pipe in on this for you.

I have actually been in this situation a few times locally as I fly in and around the Philadelphia Bravo and usually take flight following for the advisories and incase I want a bravo transition.
Its important to note that flight following does not mean you are on an IFR flight plan or that you are under ATC vectors it simply means that ATC will give you advisories (mainly traffic and often weather when applicable). Technically you are free to fly around at your discretion (within the limitations of the airspace and regulations of course).
To request flight following in this case you can say

...
  Requesting flight following to KDAY via EON

This provides enough information for them and the note that you will be taking a non direct course.
Since you are not requesting a Bravo clearance in your case its assumed you will go around (or fly under the shelf) and could potentially state only your destination. On light load days if in the system in the Philly area controllers will even warn you of the bravo if you have not requested clearance or are planning to fly under the shelf.

Thanks; sounds like you’ve done essentially this. I realize that VFR flight following is at the discretion of the controllers along the way. I usually get FF when I go, but I’ve also gotten questioned when I’m not following the most direct route.

I have done it many times, I also often, out of habit, request altitude changes when on FF only to be reminded by the controller "you are VFR altitude at your discretion"

Approach may assume you want a Class B/C transition if that's the most direct route to your stated destination, especially if you're headed directly at the boundary.  +1 for "via" as a way of telling them concisely in advance not to assume that, which avoids annoying them and getting a "say intentions" request.  Annoying someone who gives service at their discretion is unwise.

Here's a long-winded answer for a long-winded route.
Background
First of all: If you file a flight plan and select "VFR" the flight plan goes to Lockheed Flight Service only. ATC knows absolutely nothing about the flight plan; the only benefit you get is that when you run out your ETA and don't call to close the flight plan, someone will start looking for you.
When you call a Terminal controller (tower or TRACON) for VFR flight following (whether on the ground or airborne) we will make an entry in the radar system that looks like this:

Callsign
Destination (or if airborne, [approx nearby airport]*Destination)
Type code
Enroute altitude
ENTER

for example
N12345
MSN*DAY
C172
075

What this actually does is create an ATC flight plan (not a VFR/FSS flight plan!) as if you were IFR direct from your departure airport to your destination airport, but where your altitude might be 070 for IFR flight your VFR altitude is instead VFR/075. The VFR/ prefix tells the system not to apply IFR separation to your tag, so the low-altitude alert will not fire and the system will not "snitch" on the controller if you get within three miles of an IFR aircraft.
Once you tag up, the system tracks you; your flight strip will print out at various control positions along your route of flight as you get near to each controller's airspace.1 Again, this will be based on a direct line from your departure airport to your destination airport.
1If the facility still uses paper strips. Either way your callsign and approximate entry/exit fixes will show up on the scope in the "tab list."
Analysis
Let's look at your planned route vs direct:

Cross-referencing this against a map of TRACON airspace, and double-checking by looking at various airports along your route of flight (the instrument approach plates will list the relevant control facility), it looks your planned route will take you through: MSN, RFD, C90, ZAU, GUS, possibly IND and/or ZID, CMH.
But a direct route would take you through MSN, C90, SBN, FWA, CMH. That's certainly different! And it's expecting you to go through different areas of those approach controls too.
This means when the Madison controller sees you nearing Rockford's airspace and tries to hand you off, the system will flip out because it thinks you should be going through Milwaukee's airspace instead. So the controller will go to a separate terminal that communicates with the mainframe at Chicago Center and will amend your route to show you going over some fix to the south of Madison, possibly even JVL (which you're actually navigating towards). Then the system thinks you're going direct MSN..JVL..DAY and allows you to be flashed to Rockford.
This process will have to be done by each facility you go through, and possibly by more than one controller per facility. What a pain!
Solution
In a case like this, where your route has so many turns, I might suggest filing a flight plan and selecting the "IFR" option instead of "VFR." This will ensure your flight plan is sent to the Air Traffic side of the operation instead of (just?) to FSS. For altitude you should enter your desired VFR cruising altitude, ideally prefixed with VFR/ if the system allows you to do that. If you are able to enter that prefix it will be very clear to the Clearance Delivery controller what you're trying to do. Then call up CD when you're ready and say something like

Clearance, N12345, request VFR squawk code to Dayton.

The same timing "rules" would apply to your flight plan as for an IFR flight plan, namely: The strip will not print out until 30 minutes before your proposed departure time (though the controller can amend the time and make the strip print sooner if you ask them to) and the flight plan will "time out" and be deleted if you aren't airborne two hours after your proposed time.
If you can't enter the VFR/ prefix in the flight plan form, at least enter the VFR cruising altitude. Then when you call Clearance, tell them you want to amend your altitude to be "VFR at x,500," for example:

Clearance, N12345, I have an IFR on file to Dayton, request flight following on that route flying VFR at 7,500.

Now they have to go and amend your altitude once instead of every controller you talk to having to amend your route. I think I saw this the other day, actually, because I had an overflight come through my airspace VFR with a whole bunch of fixes already entered on the flight plan and the altitude was just 075 without the prefix—and the strip didn't have an amendment number on it, meaning it hadn't been touched since the pilot filed it.
NOTE ON BOTH OPTIONS ABOVE: The FAA has issued an LOI saying that doing this shows "clear intent" to violate 14 CFR 61.3(e) if the PIC does not have an instrument rating, so use at your own risk. The LOI seems to say that even if you enter a VFR cruising altitude and put "VFR" in the remarks, checking the "IFR" box counts as filing an IFR flight plan—which sort of makes sense, but also doesn't, because the real difference is not "IFR" vs "VFR" but "Air Traffic" versus "Flight Service." Speaking as a controller, this LOI is backwards and unhelpful, and your filing this way would make things easier for everyone—but they pay me to separate airplanes, not issue legal opinions.
In the case of a simpler route, say MSN-CID by way of RFD (you want to do some sightseeing?) you could just tell the controller that when you make your initial request. Not a big deal to enter in one fix one time, and in fact the controller should in theory be able to enter a single intermediate fix even when using the radar keyboard... but this doesn't work at my facility. As abelenky points out, you could do it this way and say your route is MSN..EON..DAY or MSN..JOT..DAY, either of which line up pretty nearly to your more precise plan.
Or in a much simpler case, like MSN-RST by way of LSE (ten degrees difference on-course from MSN), don't even bother mentioning it unless they ask.

Could a controller pull up a flight plan on request like that if it was filed as VFR, not IFR?

@UnrecognizedFallingObject no, there is no way for us to retrieve a flight plan filed as "VFR." (I gather there is an option, VFR or IFR, when you file?) The VFR flight plans only go to FSS. This method would be to select "IFR" but for altitude enter "VFR/075" or failing that "VFR" in the remarks section and clarify on initial callup. Though I am seeing here: https://aviation.stackexchange.com/a/37330/54557 that the FAA has issued an LOI saying they would interpret this method as showing "clear intent" to violate 14 CFR 61.3(e), so use at your own risk if you don't have an IFR cert.

I'm not yet IFR rated, so I couldn't file an IFR flight plan. I see where that would make things easier for controllers, but if I can't technically do it, it sounds like it might make controller's job easier by saying "MSN-EON-DAY"?

@JimJarrett yes, that would be the second-best (and apparently safer-for-your-certificate) option from a controller's standpoint. If you tell the MSN ground/clearance controller and they have the foresight to amend your route before you depart, the radar controllers shouldn't have to deal with it.

@randomhead hopefully within the next month or two the former becomes an option :D

This answer illustrates the immense value of having a controller participating here on Av.SE -- thanks for a great answer, randomhead!

I would make the request as:
(controller) "N12345, Say your request"
(you) "N12345 request VFR Flight Following from Madison via the Joliet VOR to Cox Dayton; Altitude 5,500"
I don't think all the intermediate points matter, and I think the controller will quickly figure out what you intend.
They may ask for some clarifications, such as:

"Say your equipment"(they're asking if you have a Mode C transponder)
"Spell waypoints"(they want the phonetic alphabet of your waypoints because they are unsure)

Who exactly are you talking to in your last example? As far as I know, ATC never sees VFR flight plans.

(I'm not 100% sure) I believe that ATC (if not too busy) can open your plan for you, see your filed route, and start FF based on your plan.  They won't see it unless you ask, but they can pull it up.

See this answer; in the linked video a controller says they don't have flight plans "in our system" but I guess they can get access somehow if they have an urgent need

(Removed the last example)

In the Center environment, it's probably best to simply make your request on the frequency,whether you've filed a VFR flight plan or not. Most VFR flight plans are filed through FSS, and are entered in their database, but are not transmitted to an FAA facility. If you were to file a flight plan with an altitude of say, 115, with "request VFR FF" in remarks, that would pass to the Center. The controller would recognize it for what it is, but the FAA, as mentioned above, would not take kindly to it.
For our purposes, we can obtain the necessary information for an abbreviated flight plan  from you on the frequency. Takes less than a minute in most cases.
In your case, we'd need your call sign, type aircraft and equipment, and destination for a VP type of flight plan. If you give us your full route (KMSN..JVL..KARR..JOT..EON..KRZL..OKK..MIE..KDAY), I (personal technique) would enter it all in the database, but most controllers will enter the VP as direct to destination, and amend the route later, as needed.
If you told me, however, that you wanted to avoid a terminal area to the south, I'd do a (very simple) re-route around the terminal area. After that, if you went farther away, or closer, than I anticipated, I'd correct the route, possibly asking what your plans were, just to clarify.
The route information only needs to be precise enough that I can ensure the correct sectors get the information they need. Out west, in my airspace, you may go 50 miles off course to look at Carhenge before going on to Rapid City. It's all in one sector, so it doesn't matter much if your route is completely accurate. Around KORD, sectors are much smaller, and a controller may need more precise routing information to ensure everyone gets their data.


text:
How are turboprops and other propeller planes pressurized?
I know how most turbofan jets are pressurized:

But it can't be the same with turboprops, as I don't understand how propellers can take in the air. Yet, planes like Q400s can fly above 8000', all the way up and higher than FL220!  Can somebody explain how this is possible?

Where did you get the idea turboprops can't take in air? A turboprop is a type of turbine engine.

It is exactly the same for turboprops.

Are you thinking of pressurized non-turboprop (non-turbine-driven) piston propeller planes? In which case, does this QA help? https://aviation.stackexchange.com/questions/38115/are-there-any-pressurized-piston-engine-aircraft

You know... a turbofan engine is a turboshaft engine that drives a fan.  They don't take bleed air off the fan, they take it off the turboshaft's compressor stages.  A turboprop engine is just a turboshaft engine that drives a prop. Same difference, really, just one looks cool.

And even some jets (google "787 no bleed air") now use plain old electric air compressors, instead of turbine bleed air. Apparently it's cheaper, but some passengers believe it's better for air quality, too,

A turboprop plane can be pressurized in the same way a turbofan plane can: via bleed air from the compressor stage of the turbine engine. A turboprop and turbofan are not that different actually. You have a turbine engine core that powers the big fan at the front or the big propeller via a gearbox (although the turbofan still gets some of its thrust from the engine core, but the turboprop does not):

(image source)
On the Dash-8 Q400 for example, the engines provide bleed air for pressurization:

The aeroplane is pressurized by engine bleed air supplied to and distributed by the air-conditioning system. Pressure is maintained and controlled by the cabin pressure control system which governs the rate of
  outflow from the pressurized areas (Figure 12.2-10) of the aeroplane. An aft outflow valve primarly
  controls the outflow of air, and is assisted by two safety valves.

(Dash-8 Q400 FCOM - Air Conditioning and Pressurization 12.2.2.1)

Air entering at the engine inlet is directed rearard and compressed (Figure 12.23-1). Two
  compressors carry out compression for combustion and bleed extraction purposes. Air is first ducted
  to the low-pressure (NL) axial compressor and then to the high pressure (NH) centrifical compressor
  where it undergoes a seconds stage of compression.

(Dash-8 Q400 FCOM - Power Plant 12.23.3.1)
The following image shows the bleed port in the PW150A engine as used on the Dash-8 Q400:

(image source)

I cannot believe that a document as serious as an aircraft accident report has been produced using Comic Sans.

Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo compressor to pressurize fresh air from the outside:

Modern aircraft with supercharged piston engines simply use bleed air from a) the main engine's compressor or

b) the main engine's turbo charger

Another solution is to drive dedicated air compressors to pressurize the cabin. Typically this may be Roots blowers or centrifugal fans. They are mechanically driven from the main engine(s).

Image source and more information on this topic: www.aircraftsystemstech.com

I was a P-3 Flight Engineer and the Allison T-56 engines had engine driven compressor's mounted on the propeller gearboxes on the inboard engines that allowed for a 30'000 ft. Ceiling.

This directly answers the question presented. First-hand stories and knowledge are valuable.

With a decade of flying Herks with T-56's, I've never heard of a compressor mounted to the gearbox. What advantage over bleed air does that provide to be worth the extra equipment?

I am actually pretty curious about this now as well. These guys mention repairing an EDC (engine-driven compressor) for the P-3. http://blueaero.com/p-3/

I added a specific question if you would like to elaborate: https://aviation.stackexchange.com/questions/77696/why-does-the-p-3-orion-use-an-engine-driven-compressor-instead-of-bleed-air-for

Piston powered aircraft can also be pressurized, the models that are have turbo-superchargers, an exhaust driven turbine that pressurises the air going into the cylinders.
Some of the air from the turbos goes to the passenger cabin. The level of pressure is controlled by outflow valves just like jet powered aircraft.


text:
Shall We Consider Reversers in performance Calculations?
Thrust reversers are featured to help slow down the plane after touchdown.
Moving the thrust levers aft activates the translating cowl to open, closing the blocker doors. This action stops the fan airflow from going aft and redirects it through the cascade vanes, which direct the airflow forward to slow the aircraft.
My question is Shall We Consider Reversers in performance Calculations ?

What do you mean "shall we"? Are you asking, "do we" in the AFM/QRH, or "should we" in future regulation amendments?

For airplanes certified under Part 23, both takeoff (AMC 23.55b) and landing (AMC 23.75f) performance can take credit for thrust reverser (T/R) if it's shown to be reliable and safe. As detailed in AC 23-8C, much extra work would be required to take credit for T/R for multi-engine airplanes:

For accelerate-stop distance: demonstration of full T/R with one-engine-inoperative and in a 10kt crosswind and on wet runway for adequate lateral controllability is required.
For landing distance: the landing distance used must be that with one-engine-inoperative; differential braking needed to maintain lateral control for this situation may negate most, if not all, of the advantage of a single T/R.

For airplanes certified under Part 25, only takeoff on wet runway may take credit for thrust reverser (25.109f). Similar situation for landing distance as with Part 23, 25.125c)3) allows credit for T/R, but only for that with one-engine-inoperative; therefore, the same problem as discussed before applies.

I've flown aircraft that do take credit for reverse thrust in their stopping performance computations, and I've flown aircraft that do not. Both FAA certified. I have no idea how to answer "shall we..." in the question, but it's certainly possible to go either way on the calculations.
Maybe the best answer is, you should know the factors and assumptions in your aircraft's performance manual.


text:
What is the purpose of the hold at JNC on the Grand Junction Seven SID?
There is a hold on the Grand Junction Seven SID.

I would expect it is there so that ATC could hold you until you reach the enroute MEA but there is no written reference.
So, what is the reason for the hold?  It is certainly not obvious from the plate or departure procedure.

I edited the question to clarify what you are asking. Try to keep the question on point and use formatting and images to make your question clear.

If you look at the chart, you'll see that after takeoff you will arrive at JNC from either the east or the northeast. Transitions then proceed back in an easterly direction (045 to 113 degrees).  With the possible exception of the Rwy 29 departure with the BRICK transition, the SID requires a course reversal at JNC. The charted hold provides a means and protected airspace for the course reversal.
And as you surmise, some aircraft may require climbing in the hold to reach the MEA.

I'm a little surprised there's no mention of the hold-in-lieu-of-PT in the textual description.

Thank you for the response but where did you pick up the idea that it "requires" a course reversal. It may become a useful tool for atc but it is not expressly required that I can see.  The procedure is "thence" but no reference to the reversal.I agree that I may be a tool to be used to climb to the mea but are you saying the course reversal is implied due to direction?  It is not specifically written anywhere.


text:
What aircraft is in The Do’s music video?
There is a band call The Do, in one of their videos there is a plane with a strange configuration of turbines, it looks like a version of a 747.
You can find the video on Youtube "The Dø - Despair, Hangover & Ecstasy"
Does anyone know what plane it is?

I can't edit this question because it has a pending edit, but if it hasn't already happened by the time the edit is reviewed, you can add this URL to the question: https://www.youtube.com/watch?v=eAXmgId3NTQ It's the song the question is talking about.

This looks like G-BDXJ, a modified 747 that was also featured in James Bond Casino Royale as well as other movies.
Edit: The linked wikipedia page confirms this:

It was used as a prop in the music video of The Dø song "Despair, Hangover & Ecstasy"

This plane is now a non-flyable movie prop

"Fake non-standard engine configuration" is a heck of a phrase


text:
Can you broadcast a very low power nav vor signal in air?
Are there any FCC restrictions on broadcasting a test nav signal on 108.0 in the air? Or perhaps on other nav frequencies that can be received within the navigation band?

What kind of transmitter are you talking about, certified equipment or experimental?

"Are there any FCC restrictions". The restriction is you need to ask for permission, and be delivered a license for operation, or a temporary permission. Conditions will be associated with the license/permission.

The answer is yes with the caveat that there are limits. The hard part in dealing with aviation radio systems is that there are multiple agencies with some overlapping regulatory authority.
As bogl points out, the ITU is the international forum for radio spectrum. The NTIA is the US agency that is the US representative to the ITU. The NTIA has general oversight of radio spectrum. Actual management of radio spectrum is delegated to various government organizations.
The FCC is the primary US manager of spectrum, but not the only one. The FAA and the military both have significant pieces of spectrum that they manage. For the FAA, these include the aeronautical radio navigation bands and the aeronautical radio communication bands. The VOR/ILS are within the VHF radio-navigation band of 108.00 to 117.95 MHz.
The FAA controls transmitting of navigation signals. They do allow for low power transmissions for the purpose of testing avionics. But you just can't build your own transmitter unless you're willing to go through a ridiculously lengthy approval process that includes both the FAA and the FCC. The FCC is involved because any transmitter has to comply with Part 15 for non-interference.
So, if you are using an approved piece test equipment you can use it for short periods of time to test avionics. The use of nav/comm ramp testers such as the IFR-4000 is quite common.

The NTIA is responsible for the Federal government's (including DoD, FAA, etc) use of the radio spectrum. The FCC is responsible for everybody else. Both work with the ITU with regards to their specific interests, but given the ITU is part of the UN, the ultimate representative is the State Department.

The use of radio transmitters is strictly controlled almost everywhere in the world. FCC would be the authority in charge if you are asking for the USA.
The International Telecommunications Union (ITU) is in charge of allocating frequency bands for different applications in the radio spectrum. You are only allowed to transmit if you have a frequency assignment, if your equipment is certified, and you are holding the required radio license.
There are use cases where non-certified equipment may be used (e.g. amateur aka HAM radio), or no license is required (e.g. wireless consumer devices like cell phones, remote controls, etc).
108.0 MHz is at the upper edge of the frequency band allocated to FM radio broadcasting, and the lower edge of civil aviation frequencies. Therefore 108.0 MHz is not available for experimental navigation signals. Your usage would be illegal. The same will be the case for any other frequency that can be used with certified navigation receivers.

+1, but you should explain how harmonic attenuation is handled too, else I can use a 27 MHz transmitter (legal without license) to create a 108 MHz signal (4th order harmonic) which is illegal without a license. By the way, all transmitters (all oscillators and heterodyne mixers) create byproducts, so everyone is actually transmitting in many bands not allocated, but at very small power.

@mins, thanks for the input, but as long as the OP doesn't bother to tell us if his equipment would be experimental or certified, I do not feel motivated enough to expand my answer.


text:
Can I work civilian aircraft with just an FAA Airframe certificate?
I am currently in the Air force, but plan on separating after my contract ends. I really like the field of avionics and aviation in general.(I am a B-1 Offensive Avionics Systems guy) However, when I went to my local FSDO, he told me I was not elegible to pursue the Powerplant portion of the A&P certification. I decided the Airframe was better then nothing, but am concerned about future employment requiring the full A&P licensure. I am a hard worker and would definitely, given the opportunity, use my time wisely to get the OJT needed to be eligible for the Powerplant part. Are there jobs in this field for someone with just the Airframe certificate?

Why are you not eligible to pursue the P portion of an A&P? I'm pretty sure I could sign up for classes and get an A&P if I wanted to and all I know about aircraft is what I've read here. What's preventing you from signing up for classwork and/or reading/learning on your own?

It's required to have 18 months of extensively record Powerplant experience in order to qualify to take the FAA Tests.  Since my primary AFSC is not in the field of Powerplant, it's near impossible for me to qualify even if crossed train. I would have to have not only 18 month OJT, But also accomplish this under an A&P licensed mechanic who would sign for me. I am trying to get the certificate, not enroll in a associates degree program.

Ah, I see. Sorry, not familiar with the regulations there.

Are there jobs for someone with just an airframe rating?
The answer to that is yes. While having both A & P ratings is a definite plus, there are places where a powerplant rating isn't necessary. There are many businesses that work with just avionics or interiors or structures, or departments segregated from powerplant. For jobs in these businesses (or departments) a powerplant rating is irrelevant.
And if you get to working at the component level, those shops (certificated repair stations) operate with Repairmen certificates. These are tied to being employed by the repair station and are generally obtained by completing specific in-house training (ref. Part 65 Subpart E). I spent the majority of my non-AF career in avionics design and manufacture. The airframe certificate was only needed by the group doing installations. All the other technicians operated with a repairman certificate.
You could also seek out an business that allows you to work primarily in airframe and train in powerplant at the same time. Or just work in airframe and take classes part time to add the powerplant later.


text:
Which fighter jet is this, based on the silhouette?
6 to 8 of these planes flew through the Ogwen Valley in North Wales, UK, this morning (2nd of June). Hawks and other training jets are common sights, but I’ve not seen these before and can’t identify the model. I thought F35s from the distinctive tail, but the wings are more swept back than the images of F35s I can find.

Good job on getting a crisp photo.

@BowlOfRed Got quite a few, and a video. After the first one shot by, I was ready to go.

Judging by the tail and its therefore unnecessary wing(s).... The air intakes are a dead give away tho.

One of my favorites!

What you've got there is a real life F-15! Love this aircraft, it's just got that quintessential military jet look about it.
There are 2 features which make it stand out

The shape of the trailing edge of the main wings, straight and then angled

The shape of the tailplane, with those jagged leading edges

Silouette of an F-15:

Thanks. Me and my mate actually worked it out in the end. I was only looking for planes operated by the RAF, but of course there are F15s stationed at Lakenheath.

Probably increasing operational frequency in anticipation of training Ukranian pilots.

@A.I.Breveleri or even being flown by those Ukrainian pilots?

"it's just got that quintessential military jet look about it."  The F-86 Sabre is the fighter jet look (though maybe just for old people), with the F-4 Phantom a close second.

That's a United States Air Force F-15E Strike Eagle, most likely one of those that are based at Lakenheath.

We reached the same conclusion in the end. Thanks.

Looks like an F-15E Strike Eagle

F-15 silhouette
Twin seat
Dark grey uniform paint scheme
‘Twin bagger’ ie 2 x 600 gal external tanks
No missiles on the rails.
Difficult to see if it has the FAST packs on the side of the fuselage
Modern P&W F100 engine variant with the ‘turkey feather’ exhaust petals removed.
Difficult to see from this angle the discerning features that separate it from an F-15D.

But…

Most likely a Strike Eagle bubba out of Lakenheath doing some low level practice.


text:
Is it true that Grodno airport recently got a higher category? What is it, what does it mean?
Grodno Airport (IATA: GNA, ICAO: UMMG) is an airport that serves Grodno, Belarus. It is close to the European Union border and Polish politicians says Belarus plans to use it to make the EU immigration crisis worse, because Belarus just changed its category:

The airport in Grodno was given a higher category by the authorities. [...]
The Belarusian authorities have decided that the airport in Grodno will have the status of an airport where international flights can take place [...]

(kresy24.pl, translated by Google)
Political issues are the reason for this question, but I'm not interested in that part here. I want to know the raw facts - did this change happen? And what does it mean in terms of passenger volume, flight distances etc.? What actually changed, if it changed at all?

Define "higher category."

@JuanJimenez wish if I knew. I can't just go ask members of my government what they meant by category, I'm just a regular guy. I guess everything that affects how far flight it can accept or how many people can go though monthly should count.

Do you have an article or something that quotes the exact language used?

For example: https://kresy24.pl/lotnisko-w-grodnie-dostalo-od-wladz-wyzsza-kategorie-bezposrednio-przy-naszej-granicy-mozemy-sie-spodziewac-lotow-z-migrantami-z-poludniowej-czy-z-polnocnej-afryki/

FWIW, Wikipedia says "Since 1993, the airport is allowed to perform international flights." Not sure what category they are talking about.

EU-Belarus border crossing background. On the question itself, categories relating to international airports are used, e.g. for Australia. It mostly deals with prior approval for the flight.

@Mołot The problem with your question is that the term "higher category" is meaningless in an IATA context, so any answers are likely to be opinions. You might want to write to the media outlet or the author or the piece to ask for an explanation of what that means.


text:
Is the turn radius at fixed bank angle really independent of aircraft type?
I'm curious about the relationship between an aircraft's turn radius and the bank angle. This formula describes the relationship between the two:
$$ R = \frac{v^2}{g \tan(b)} $$
Where $R$ is the turn radius, $v$ is the speed, $g$ is acceleration due to gravity and $b$ is the bank angle.
This formula is found dotted around the internet (with variations depending on units used) examples include here and here.
My question is, why is there no reference in the formula to the physical characteristics of the aircraft? Does the relationship between turn radius and angle-of-bank really have nothing to do with aircraft weight, wingspan or aerofoil design? Does the same formula really hold true for both glider (sailplane) and large passenger jet?
Hoping for an explanation with no maths please!

Related: https://aviation.stackexchange.com/questions/58504/what-is-the-derivation-of-15-and-11-3-used-for-computing-pivotal-altitude

be careful. Be Clear.. Are you asking about actual turn radius at some specific flight condition? or are you asking about the minimum (best possible) turn radius? The former is totally independent of aircraft characteristics, weight, wing loading, etc. The formula (if you replace g tan(b) with Gr (radial G), even applies to turn radius on a merry-go-round.  Best Possible (minimum) turn radius, on the other hand is absolutely dependent on aircraft characteristics and aerodynamic capabilities,.

Why is there no reference in the formula to the physical characteristics of the aircraft?

In level steady state flight Weight = Total Lift = Vertical Lift.  The ratio of Total Lift to Vertical lift = 1.  In a bank more lift must be generated to maintain sufficient vertical lift.  The ratio of Vertical Lift to Horizontal Lift is Tangent (bank angle).  The horizontal lift component is what changes the direction of the flight path.  The Force moving it in a new direction is mass x acceleration.  This is always proportional the lifting force regardless of weight.
As lateral motion accelerates from zero and direction is always changing, the side drag of the aircraft is not nearly as significant as the sideways acceleration compared to the energy of forward motion.
Here the "physical characteristics of the aircraft" are accounted for in Velocity: the sailplane has a much tighter turning radius than the jet airliner because of a much lower stall stall speed.
This is where airfoil type and wing loading come into play.
The key to understanding this is to put mass "m" back into the equation:
R = mv$^2$/mg (tan bank angle)
We can now clearly see the energy of the object is proportional to the square of the velocity.  Weight (therefor lift) is mg.  One simply gets a slower rate of turn with
a faster moving object for a given amount of sideways acceleration.
Now, if one cuts power and wants to turn, physical characteristics of the aircraft will matter.  Broad, low aspect, draggy wings make biplanes more maneuverable in turns than their faster mono plane counterparts.  This is one reason triplanes were all the rage before new tactics were developed.

If the turn is fully coordinated, turn radius at a given bank angle will depend on the speed of the aircraft and the local value of gravity.
This is because of simple vector and geometry: the vertical component of lift must still support the weight of the aircraft (whether that's a hang glider or an AN-225, a Helio Courier on the edge of stall or an SR-71), but the horizontal component, generated by the bank, produces a horizontal (=> centripetal) acceleration that is fixed in relation to gravity for a given bank angle.
The problem is that this centripetal acceleration is determined by both turn radius and speed.  So, if your hang glider and your SR-71 want to make the same radius turn (within their usual flight envelope), they'll do it at wildly different bank angles.

Wrong. It has nothing to do with the "local value of gravity" the g in the equation is not gravity, it is the radial acceleration - G-radial, or Gr. The actual formula is V2/Gr.  The formula in the question  uses bank angle because g tan(b), where b is the bank angle is a formula for G-Radial (the acceleration of the aircraft in the direction of the turn). And your hang glider and your SR-71 if they were flying in formation (If they could both fly at the same speed) would need to be at exactly the same bank angle to remain in formation with one another.

@CharlesBretana Better draw your force diagram again.  The vertical component of lift will always be the local gravity * mass of the aircraft (taken as fixed; we discount fuel or stores expenditure burn for this).  Therefore centripetal acceleration at a given bank angle depends on local gravity -- if your local gravity is lower (as for instance flying on Mars), you'll have less horizontal acceleration for a given bank angle than you'd have on Earth.

Yes, my comment is perhaps slightly misstated. What I was trying to say is that implying that the local force of gravity affects turn radius in a horizontal turn is incorrect. The formula, using radial G, (Gr), instead of g Tan(b), always applies, for anything on a curved path. The g in the g Tan(b) expression is there because Gr = g Tan(b), (a shortcut to calculate radial G from bank angle), not because the local force of gravity is relevant. Indeed, in uncoordinated flight, or if some other force is augmenting the turn, (or on another planet), it would be wrong. Using V2/Gr will always work.

The force diagram is also irrelevant, as it only serves to justify the use of the shortcut to calculate radial G from bank angle. It has no relevance to the calculation of the curvature (radius), of the path traversed by a moving body. That is determined by velocity (squared) divided by radial G, - i.e., the normal acceleration (component of acceleration in the radial direction).

Assuming your turn doesn't involve vertical acceleration (it shouldn't, if correctly coordinated), local gravity is still in the mix.  You vertical component must still be the same as local gravity, which constrains the horizontal to be dependent on bank angle.  Draw your force diagram until you understand what you're arguing.

Look at the formula again. Turn radius equals velocity squared divided by radial acceleration. Where is local gravity?  Not there, is it? A basic rule of Physics is that when analyzing a problem in multiple dimensions, the analysis for each dimension is totally independent of all the others. I.e., every dimension can be analyzed without reference to the others. So on a HORIZONTAL turn, the"vertical component" of anything does NOT have to be the same as anything else, (as your need to add caveats for uncoordinated flight, aircraft mass, etc. make clear.)

local gravity constrains horizontal acceleration at any given bank angle.  If you're banked at 30 degrees, you have to pull 1/.866 G to stay level, and you get 0.5 G horizontal.  But if you local G is 0.4 (as on Mars) you're pulling 0.4/.866 to stay level, and get 0.5*.4=.2 horizontal, hence a much larger turn radius at the same bank angle and speed.

Your comment is false. As we are talking about the formula for ACTUAL turn radius, not minimum turn radius for a specific aircraft, local gravity dies NOT constrain horizontal acceleration. I could add a rocket motor to the side of my aircraft. I could cant the engines at a fixed downwards angle, (or adjustable like the Harriet or F-22/F-22), etc. etc. Indeed if you start taking about stuff like that, and then bring up Mars, you need to address the fact that the atmospheric density there is equivalent to Earth at 110,000 feet.

Let us continue this discussion in chat.

Let's not and say we did.


text:
Can RNP AR APCH be defined as NPA or APV or PA?
How to define RNP AR APCH as a

Non-Precision Approach / Approach with Vertical Guidance / Precision
  Approach?

or it varies when complying with different standards just like RNP APCH?
or it's only a special navigation method?
A document published by Airbus Safety First says:

RNP and RNP AR procedures allow crews to fly approaches using internal
  and very accurate navigation tools, instead of traditionally using
  external guidance aids. They also allow the replacement of visual and
  circling approaches by instrument approaches, thereby enhancing the
  safety of airline operations. They are non-precision approaches
  although they provide the crews with cues and procedures similar to
  those used on precision approaches.

Click here, the
 2nd paragraph in  Introduction Part https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/performance-based-navigation-rnp-and-rnp-ar-approaches.pdf
How can it define RNP as only a NPA?

They are non-precision approaches with vertical guidance.  So, they would be considered an APV approach. From what I recall about ICAO Annex 10, only ILS and MLS are classified as a precision approach.  A PAR approach may also be considered a precision approach.

So there is no official document mentioning the classification of RNP AR APCH, and what we can only classify is whether it's using vertical guidance or not?

Yes, you are right. I found "RNP AR APCH operations are classified as approach procedures with vertical guidance (APVs) in accordance with Annex 6 — Operation of Aircraft. This type of operation requires a positive vertical navigation (VNAV) guidance system for the final approach segment (FAS). Current RNP AR APCH implementations utilize a barometric vertical navigation system (BARO-VNAV) meeting specified airworthiness requirements. " in DOC9905 1.2.3 at ICAO. link here:https://www.icao.int/Meetings/PBN-Symposium/Documents/9905_cons_en.pdf


text:
737 ALT DISAGREE Non-Normal Checklist questions
1 choose IAS DISAGREE alert is not shown, and then:
2 Verify all altimeters are set to correct barometric setting.
3 choose DISAGREE alert stays illuminated:
and here is the thing, WHY 4 Standby altimeter is available?
How to know standby altimeter is available?

That statement is a reminder that you have the standby altimeter available as a resource.  It's not accurate enough to allow you to stay in RVSM airspace, but it may be a tie-breaker between the disagreeing instruments.  And for a crew that is so focused on the displays and wanting to sort our what should be believed and what should be ignored, that sort of a reminder may be what's needed in the stress of the moment.

This is a great human factors answer!